// synch.cc 
//	Routines for synchronizing threads.  Three kinds of
//	synchronization routines are defined here: semaphores, locks 
//   	and condition variables (the implementation of the last two
//	are left to the reader).
//
// Any implementation of a synchronization routine needs some
// primitive atomic operation.  We assume Nachos is running on
// a uniprocessor, and thus atomicity can be provided by
// turning off interrupts.  While interrupts are disabled, no
// context switch can occur, and thus the current thread is guaranteed
// to hold the CPU throughout, until interrupts are reenabled.
//
// Because some of these routines might be called with interrupts
// already disabled (Semaphore::V for one), instead of turning
// on interrupts at the end of the atomic operation, we always simply
// re-set the interrupt state back to its original value (whether
// that be disabled or enabled).
//
// Copyright (c) 1992-1993 The Regents of the University of California.
// All rights reserved.  See copyright.h for copyright notice and limitation 
// of liability and disclaimer of warranty provisions.

#include "copyright.h"
#include "synch.h"
#include "system.h"

//----------------------------------------------------------------------
// Semaphore::Semaphore
// 	Initialize a semaphore, so that it can be used for synchronization.
//
//	"debugName" is an arbitrary name, useful for debugging.
//	"initialValue" is the initial value of the semaphore.
//----------------------------------------------------------------------

Semaphore::Semaphore(char* debugName, int initialValue)
{
    name = debugName;
    value = initialValue;
    queue = new List;
}

//----------------------------------------------------------------------
// Semaphore::Semaphore
// 	De-allocate semaphore, when no longer needed.  Assume no one
//	is still waiting on the semaphore!
//----------------------------------------------------------------------

Semaphore::~Semaphore()
{
    delete queue;
}

//----------------------------------------------------------------------
// Semaphore::P
// 	Wait until semaphore value > 0, then decrement.  Checking the
//	value and decrementing must be done atomically, so we
//	need to disable interrupts before checking the value.
//
//	Note that Thread::Sleep assumes that interrupts are disabled
//	when it is called.
//----------------------------------------------------------------------

void
Semaphore::P()
{
    IntStatus oldLevel = interrupt->SetLevel(IntOff);	// disable interrupts
    
    while (value == 0) { 			// semaphore not available
	queue->Append((void *)currentThread);	// so go to sleep
	currentThread->Sleep();
    } 
    value--; 					// semaphore available, 
						// consume its value
    
    (void) interrupt->SetLevel(oldLevel);	// re-enable interrupts
}

//----------------------------------------------------------------------
// Semaphore::V
// 	Increment semaphore value, waking up a waiter if necessary.
//	As with P(), this operation must be atomic, so we need to disable
//	interrupts.  Scheduler::ReadyToRun() assumes that threads
//	are disabled when it is called.
//----------------------------------------------------------------------

void
Semaphore::V()
{
    Thread *thread;
    IntStatus oldLevel = interrupt->SetLevel(IntOff);

    thread = (Thread *)queue->Remove();
    if (thread != NULL)	   // make thread ready, consuming the V immediately
	scheduler->ReadyToRun(thread);
    value++;
    (void) interrupt->SetLevel(oldLevel);
}

// Dummy functions -- so we can compile our later assignments 
// Note -- without a correct implementation of Condition::Wait(), 
// the test case in the network assignment won't work!

Lock::Lock(char* debugName) {
  name = debugName;
  mySema = new Semaphore(debugName, 1);
  numWaiting=0;
}

Lock::~Lock() {
  delete mySema;
}
void Lock::Acquire() {
  IntStatus oldLevel = interrupt->SetLevel(IntOff);	// disable interrupt
	
	if(heldBy == currentThread)
	{
		printf("Thread %s already holds lock %s\n",currentThread->getName(),name);
		printf("Don't acquire a lock you already own\n");
		interrupt->SetLevel(oldLevel);
		return;
	}
  mySema->P();
  numWaiting++;
  heldBy = currentThread;

  interrupt->SetLevel(oldLevel); //re-enable interrupts
}
void Lock::Release() {
  if(!heldBy)
    {
     printf("No thread has acquired lock, %s, but %s is trying to release.\n",name,currentThread->getName()); //print error
    }
  else if(heldBy != currentThread)
    {
      printf("Current thread has not acquired lock %s \n", name); //print error
	  printf("Current thread: %s  ---  Held By: %s\n", currentThread->getName(),heldBy->getName());
    }
  else
    {
	  numWaiting--;
	  heldBy=NULL;
      mySema->V();
    }
}
bool Lock::isHeldByCurrentThread()
{
  if(!heldBy)
    {
      return false;
    }
  else 
    {
      return (heldBy == currentThread);
    }
}

Condition::Condition(char* debugName) { 
  name = debugName;
  queue = new List;
  numWaiting=0;
}
Condition::~Condition() { 
  delete queue;
}
void Condition::Wait(Lock* conditionLock) { 
  IntStatus oldLevel = interrupt->SetLevel(IntOff);

  if(conditionLock == NULL) //if no lock was actually passed
    {
      printf("NULL Lock passed to Condition::Wait.\n"); //print error
      interrupt->SetLevel(oldLevel); //restore interrupts
      return; //exit function
    }

  if(waitingLock == NULL) //if no lock is currently waiting
    {
      waitingLock = conditionLock; //make this lock the wiating lock
    }

  if(waitingLock != conditionLock) //if another lock set wait already
    {
      printf("Different Lock passed to Condition::Wait.\n");//print error
      interrupt->SetLevel(oldLevel); //restore interrupts
      return; //exit function
    }

  //ok to wait
  numWaiting++;
  conditionLock->Release(); //exited the monitor
  queue->Append((void*) currentThread); 
  //printf("Condition::Wait sleeping thread.\n");
  currentThread->Sleep();
  conditionLock->Acquire();
  interrupt->SetLevel(oldLevel); //restore interrupts
}
void Condition::Signal(Lock* conditionLock) {
  IntStatus oldLevel = interrupt->SetLevel(IntOff);	// disable interrupts

  if(queue->IsEmpty())
    {
     interrupt->SetLevel(oldLevel);	// re-enable interrupts
     return;
    }

  if(waitingLock != conditionLock)
    {
      printf("Different Lock passed to Condition::Signal.\n"); //print error
      interrupt->SetLevel(oldLevel);	// re-enable interrupts
      return;      
    }

  //okay to signal
  Thread* thread = (Thread *)queue->Remove();
  if (thread != NULL)	   // make thread ready, consuming the V immediately
    {
	numWaiting--;
      scheduler->ReadyToRun(thread);
    }

  if(queue->IsEmpty()) //no more waiting threads now
    {
      waitingLock = NULL;
    }

  interrupt->SetLevel(oldLevel);	// re-enable interrupts
}

void Condition::Broadcast(Lock* conditionLock) {
  IntStatus oldLevel = interrupt->SetLevel(IntOff);	// disable interrupts

  if(queue->IsEmpty())
    {
     interrupt->SetLevel(oldLevel);	// re-enable interrupts
     return;
    }

  if(waitingLock != conditionLock)
    {
      printf("Different Lock passed to Condition::Broadcast.\n"); //print error
      interrupt->SetLevel(oldLevel);	// re-enable interrupts
      return;      
    }
  //okay to broadcast

  while(!queue->IsEmpty()) //while there are waiters
    {
      Thread* thread = (Thread *)queue->Remove();
      if (thread != NULL)	   // make thread ready, consuming the V immediately
		{
		numWaiting--;
		scheduler->ReadyToRun(thread);
		}
    }

  waitingLock = NULL;
  
  interrupt->SetLevel(oldLevel);	// re-enable interrupts
}


